Embodiments of the present invention generally relate to plasma guns, and more particularly to ablative plasma guns.
Electric power circuits and switchgear typically involve conductors separated by insulation. Air space often serves as part or all of this insulation in some areas. If the conductors are too close to each other or the voltage difference exceeds the insulation properties, an arc can occur between the conductors. Air or any insulation (gas or solid dielectrics) between the conductors can become ionized, making the insulation conductive and thereby enabling arcing. Arc temperatures can reach as high as 20,000° C., vaporizing conductors and adjacent materials, and releasing an explosive energy that can destroy circuits.
Arc flash is the result of a rapid energy release due to an arcing fault between phase-phase, phase-neutral, or phase-ground. An arc flash can produce high heat, intense light, pressure waves, and sound/shock waves similar to that of an explosion. However, the arc fault current is usually much less in magnitude as compared to short circuit current, and hence delayed or no tripping of circuit breakers is expected unless the breakers are selected to handle an arc fault condition. Typically, arc flash mitigation techniques use standard fuses and circuit breakers. However, such techniques have slow response times and may not be fast enough to mitigate an arc flash.
One other technique that has been used to mitigate arc fault is to employ a shorting (mechanical crowbar) switch, placed between the power bus and ground, or between phases. Upon occurrence of an arc fault, the crowbar switch shorts the line voltage on the power bus and diverts the energy away from the arc flash, thus protecting equipment from damage due to arc blasts. The resulting short on the power bus causes an upstream circuit breaker to clear the bolted fault. Such switches, which are large and costly, are located on the main power bus causing the bolted fault condition when triggered. As a result, the mechanical crowbars are known to cause extreme stress on upstream transformers.
There is a need for improved arc flash prevention mechanism that has an improved response time and that is cost effective.